Vehicle engines typically incorporate burned gas control systems in order to reduce NO.sub.x emissions generated by the engine. As is known to those skilled in the art, the rate at which burned gas is recycled also affects the emissions, fuel economy and power output of an engine at a particular throttle position. Burned gas control systems typically take the form of an exhaust gas recirculation (EGR) mechanism which transports a controlled amount of exhaust gas from the exhaust manifold of the engine to the intake manifold to be mixed into an air/fuel mixture which is subsequently combusted. More recently, in engines with variable position camshafts, the recycling of burned gas is controlled by altering the phase angle of the camshaft to control the amount of burned gas which is recycled on a subsequent engine cycle.
Typically, the rate at which burned gas is recycled is determined by a powertrain controller as a function of the rotational speed of the engine and the air mass flow of the engine. A table which contains predetermined values for different engine speed and cylinder aircharge is accessed and a desired burned gas recycling rate value is retrieved. The degree to which engine power output required by the driver can be delivered, while meeting emissions constraints and maximizing fuel economy is dependent on a variety of factors in addition to engine speed and air mass flow into the engine. Conventional powertrain controllers, which utilize burned gas recycling, do not provide a mechanism to meet the power output required by the driver, while meeting emissions constraints and maximizing fuel economy, especially during transient operation. Instead, such systems decrease the burned gas recycling rate to assure the power output level desired by the driver. Unfortunately, this results in increased emissions and reduced fuel economy.
Accordingly, there is a need for a powertrain controller which controls the rate at which burned gas is recycled in a manner which provides vehicle power output requested by the driver, while minimizing fuel consumption and meeting emissions constraints.